Various kinds of image pickup apparatuses have been proposed and developed. For example, an image pickup apparatus including an image capturing lens, and a shutter which is divided into a right-hand side region and a left-hand side region, and open and close of which are selectively switchable every division region has been proposed. This image pickup apparatus, for example, is described in Japanese Patent No. 1,060,618 (“Patent Document 1”), Japanese Patent Laid-Open No. 2002-34056 (“Patent Document 2”), and JP-A-H09-505906. According to this image pickup apparatus, the open and close for the right-hand and left-hand side regions of the shutter are alternately switched over to each other in a time division manner, thereby switching a transmission optical path. As a result, two kinds of images (a left-hand side viewpoint image and a right-hand side viewpoint image) which are apparently obtained through the photographing from right-hand and left-hand side viewpoints by using one image pickup optical system can be acquired in the time division manner. The left-hand side viewpoint image and the right-hand side viewpoint image are offered to the eyes of the human being by using some sort of means, whereby the human being can feel a stereoscopic effect in the image.
Many image pickup apparatuses each of which can acquire the right-hand and left-hand side viewpoint images in the manner as described above by itself are aimed at a still image. In addition, the image pickup apparatus which photographs a moving image is also proposed. This, for example, is described in Patent Documents 1 and 2. Any of these image pickup apparatuses uses a so-called global shutter type Charge Coupled Device (CCD), as an image sensor, in which exposure and signal reading are carried out in a frame-sequential manner.
However, in recent years, a Complementary Metal Oxide semiconductor (CMOS) sensor which can realize a low cost, low power consumption and high-speed processing as compared with the case of the CCD has become a mainstream. Unlike the CCD as described above, the CMOS sensor is a so-called rolling shutter type image sensor in which the exposure and the signal reading are carried out in a line-sequential manner. With the CCD described above, the entire picture is collectively photographed at the same time in each of frames. On the other hand, with the CMOS sensor, because the driving, for example, is carried out from an upper portion to a lower portion of the screen in the line-sequential manner, a time lag is generated in an exposure period of time or at a reading timing every line in each of the frames.
For this reason, when the CMOS sensor is used in the image pickup apparatus which carries out the photographing while the optical path is switched by the shutter as described above, a time lag is generated between an open period of time for each of the regions in the shutter, and an exposure period of time for the corresponding frame. As a result, there is encountered a problem such that in each of the frames, a transmitted light in the right-hand side region of the shutter, and a transmitted light in the left-hand side region of the shutter are mixedly received (crosstalk is generated between right-hand and left-hand side viewpoint images), and thus images of multiple viewpoints (the right-hand and left-hand side viewpoint images in this case) cannot be precisely acquired. Because amounts of right-hand and left-hand side parallaxes are reduced when the crosstalk is generated between the viewpoint images in such a manner, a desired stereoscopic effect is hardly obtained (easily recognized as a planar image).